Kate Middleton, 37, wore the Lover’s Knot diamond and pearl tiara with the Queen Mother's sapphire and diamond fringe earrings.
The tiara is sometimes referred to as the Cambridge Lover’s Knot, but it is actually a replica of it, which was commissioned by Queen Mary in 1914 and made by Garrard.
Princess Diana was given the tiara as a wedding gift from the Queen in 1981 and Kate first wore the headpiece in December 2015 for the Diplomatic Reception.
The queen inherited her mother’s sapphire and diamond earrings after her death in 2002. Kate has worn them once before for a gala event at the Victoria & Albert Museum in 2015.
The duchess and her husband Prince William, 36, traveled to Buckingham Palace by car from their residence at Kensington Palace.
Kate paired the jewels with a white ruffled gown by her go-to fashion designer Alexander McQueen.
She also debuted her Royal Victorian Order, which she was awarded by the Queen in April in recognition of her services to the crown.
This is the tenth time we’ve seen Kate wear a tiara. On the last occasion, she wore the Lover’s Knot tiara and Collingwood diamond and pearl drop earrings for the Queen’s annual Diplomatic Reception in December.
The state banquet is being held in the ballroom at Buckingham Palace where President Trump and the first lady sat with members of the royal family and around 170 other guests.
President Donald Trump and First Lady Melania Trump with Queen Elizabeth II, Prince Charles and Camilla Parker Bowles during a State Banquet at Buckingham Palace in London. @realDonaldTrump #TrumpUKVisit pic.twitter.com/droIQpJ1qU— Doug Mills (@dougmillsnyt) June 3, 2019
Joining the president and the first lady at the white tie and tiara event are four of Trump's five children – Ivanka Trump, with her husband Jared Kushner, Donald Trump Jr., Eric Trump and his wife Lara, and Tiffany Trump.
Sixteen members of the royal family were at the dinner – the Queen, the Prince of Wales, the Duchess of Cornwall, the Duke and Duchess of Cambridge, the Duke of York, the Earl and Countess of Wessex, the Princess Royal, Vice Admiral Sir Tim Laurence, the Duke and Duchess of Gloucester, the Duke of Kent, Prince and Princess Michael of Kent and Princess Alexandra.
The Duke of Sussex, who joined the Trumps at a private lunch earlier today, was absent from the banquet.
The president and first lady arrived at London’s Stansted Airport Monday morning and were greeted by Foreign Secretary Jeremy Hunt and U.S. Ambassador to the U.K. Woody Johnson.
They were met by the Prince of Wales and Duchess of Cornwall on the lawn of Buckingham Palace, as they stepped off the Marine One aircraft. They were then taken up the steps of the West Terrace to be welcomed by the queen.
Prince Charles and the Duchess of Cornwall greet the Pres and Mrs Trump as they step off Marine One, and escorts them to the terrance to be welcomed by the Queen. pic.twitter.com/oTOn7hELkK— Mark Knoller (@markknoller) June 3, 2019
The national anthems of the U.S. and the U.K. were played, before the president and Prince Charles inspected a Guard of Honour formed by Nijmegen Company, Grenadier Guards.
Their next stop was Westminster Abbey where the couple laid a wreath at the grave of the Unknown Warrior.
The president and first lady then enjoyed tea at Clarence House with Charles and Camilla, before returning to Winfield House, which is the U.S. ambassador’s home in Regent’s Park.
Read more from Yahoo Lifestyle